The present invention relates to accessory gearboxes used in gas turbine engines. More particularly, the present invention relates to a reduced size accessory gearbox.
Gas turbine engines, such as turbofans, commonly include accessory systems, which may be distinguished from the principal engine components, for example, the fan, compressors, combustor, and turbines. One such accessory system is the accessory gearbox. The accessory gearbox is commonly driven by a power take-off shaft, sometimes referred to as a tower shaft, connected to and driven by a main engine shaft, for example, the compressor shaft. The accessory gearbox, in turn, commonly drives several engine accessories connected to the gearbox at gearbox pads. One such engine accessory driven by and connected to the accessory gearbox is an electrical generator used to power various electrical systems in the engine, as well as the onboard electrical systems of the plane to which the engine is attached. Another accessory commonly connected to the accessory gearbox is the main engine oil system, which is used to lubricate components of the engine, for example, bearing components of the compressors and the turbines. In some engine configurations, the accessory gearbox, and the accessories connected thereto, may be mounted radially outward from the main axis of the engine, aft of the fan and low pressure compressor section, and inside a nacelle around which working medium gas is driven by the fan section to produce thrust.
The size and arrangement of prior accessory gearboxes create several challenges in gas turbine engine design. In particular, the size and arrangement of prior gearboxes and the accessories connected thereto has degraded engine efficiency by necessitating a radially outward bulge in the nacelle surrounding the gearbox. The nacelle shape is important to engine efficiency, as the nacelle defines the aerodynamic surface across which working medium gas is driven from the fan section to produce thrust. The bulge in the nacelle shape surrounding the gearbox degrades efficiency by acting to remove energy from the working medium gas as it travels over the bulged surface. In modern high bypass turbofan engines, the nacelle shape is particularly important to engine efficiency, because a large percentage, for example 75%, of the thrust used to propel the engine is produced by the fan section.